1. Field of the Invention
The present invention relates to a film formation apparatus for a semiconductor process for forming a thin film containing silicon on a target substrate, such as a semiconductor wafer, and also to a method for using the apparatus. The term “semiconductor process” used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or a glass substrate used for an FPD (Flat Panel Display), e.g., an LCD (Liquid Crystal Display), by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
2. Description of the Related Art
In manufacturing semiconductor devices, a process, such as CVD (Chemical Vapor Deposition), is performed to form a thin film, such as a silicon nitride film or silicon oxide film, on a target substrate, such as a semiconductor wafer. In a film formation process of this kind, a film formation gas is supplied into the reaction tube (reaction chamber) of a heat-processing apparatus, so that the film formation gas causes a reaction and thereby produces a reaction product. The reaction product is deposited on the surface of each semiconductor wafer, and forms a thin film on the surface of the semiconductor wafer.
The reaction product generated during the film formation process is deposited (adhered) not only on the surface of the semiconductor wafer, but also on, e.g., the inner surface of the reaction tube and other members, the latter being as by-product films. If the film formation process is continued while by-product films are present on the inner surface of the reaction tube and so forth, a stress is generated and causes peeling of some of the by-product films and the quartz of the reaction tube and so forth due to a difference in coefficient of thermal expansion between the quartz and by-product films. Consequently, particles are generated, and may decrease the yield of semiconductor devices to be fabricated.
In order to solve this problem, cleaning of the interior of the reaction tube is performed after the film formation process is performed once or repeated several times. Where cleaning is performed for by-product films containing silicon, a halogen-containing acidic gas, such as hydrogen fluoride gas, is supplied as a cleaning gas into the reaction tube. The by-product films deposited on the inner surface of the reaction tube and so forth are thereby dry-etched and removed by the cleaning gas (for example, Jpn. Pat. Appln. KOKAI Publication No. 3-293726).
Where a gas containing fluorine, such as hydrogen fluoride gas, is used as a cleaning gas to remove by-product films containing silicon, various silicon-containing fluorides, such as fluorosilicate, are generated as by-products. Of the silicon-containing fluorides, molecules including six or more fluorine atoms, such as hexafluorosilicate (H2SiF6) and ammonium fluorosilicate ((NH4)2SiF6), can be more easily deposited on the inner surface of the reaction tube. Specifically, in order to vaporize and thereby remove these fluorides, it is necessary to form a vacuum and heated atmosphere of 133 Pa (1 Torr) or less and 100° C. or more. Accordingly, where a gas containing fluorine is used as a cleaning gas to remove by-product films containing silicon, the vacuum and heated atmosphere is formed inside the reaction tube during the cleaning to prevent such fluorides from being deposited, or the vacuum and heated atmosphere is formed inside the reaction tube after the cleaning to remove deposited fluorides.
However, as described later, the present inventors have found that conventional methods including a cleaning process for using a film formation apparatus of this kind have room for improvement in terms of some characteristics of the apparatus concerning the throughput and particle generation.